An 18-year-old Tibetan nun has set herself on fire in western China in the latest protest against Beijing's handling of the Tibetan regions it rules, an activist group said.

Free Tibet said in a statement that the nun had set herself on fire on Saturday and was believed to have survived. The young woman, identified as Tenzin Choezin, was a nun at the Mamae nunnery in Sichuan province's Aba prefecture, the statement said.

It said Choezin shouted slogans of protest against the Chinese government before setting herself on fire at a junction close to the nunnery.

"Soldiers and police came immediately and took her away," the statement said. "Soldiers then surrounded the nunnery and sealed it off."

As many as 18 monks, nuns and ordinary Tibetans have set themselves on fire over the past year, and Free Tibet says at least 12 have died from their injuries.

Activist groups say the self-immolations are a protest against China's policies and a call for the return of the Dalai Lama, the Tibetans' spiritual leader who fled from the Himalayan region to India amid an abortive uprising against Chinese rule in 1959.

A statement by two Tibetan monks exiled in India, Losang Yeshe and Kanyag Tsering, distributed by the International Campaign for Tibet, said Choezin was the eldest of four children and a good student.

The Mamae nunnery has a history of showing fierce loyalty to the Dalai Lama.

In October, a 20-year-old nun from the same nunnery died after setting herself on fire and a group of nuns at Mamae staged a protest march in 2008, carrying a portrait of the Dalai Lama, which led to mass detentions and prison terms for some of the nuns, the ICT statement said.

The Chinese government has condemned the self-immolations and says an upsurge in violence in Tibetan areas, including some deadly clashes between Tibetan protesters and security forces, are being instigated by forces outside the country wanting to separate Tibet from China.

China has vilified the Dalai Lama for more than a decade, accusing him of a campaign to split the Himalayan region from the rest of China. The Dalai Lama says he is only seeking increased autonomy for Tibet.

The last few months have been the region's most violent period since 2008, when deadly rioting in Tibet's capital, Lhasa, spread to Tibetan areas in adjoining provinces. China responded by flooding the area with troops and closing Tibetan regions entirely to foreigners for about a year.

China says Tibet has been under its rule for centuries, but many Tibetans say the region was functionally independent for most of that time. Anger over cultural and religious restrictions is deepened by a sense that Tibetans have been marginalised economically by an influx of migrants from elsewhere in China.